Resource Fresh water biology - useful articles and science references

[Yugang]

Attached a great review paper, in which respected scientists give an overview and references for further study.

REVIEW PAPER

Ecological imperatives for aquatic CO2-concentrating mechanisms
Stephen C. Maberly, and Brigitte Gontero

Abstract

In aquatic environments, the concentration of inorganic carbon is spatially and temporally variable and CO2 can be substantially oversaturated or depleted. Depletion of CO2 plus low rates of diffusion cause inorganic carbon to be more limiting in aquatic than terrestrial environments, and the frequency of species with a CO2-concentrating mechanism (CCM), and their contribution to productivity, is correspondingly greater. Aquatic photoautotrophs may have biochemical or biophysical CCMs and exploit CO2 from the sediment or the atmosphere. Though partly constrained by phylogeny, CCM activity is related to environmental conditions. CCMs are absent or down-regulated when their increased energy costs, lower CO2 affinity, or altered mineral requirements outweigh their benefits. Aquatic CCMs are most widespread in environments with low CO2, high HCO3−, high pH, and high light. Freshwater species are generally less effective at inorganic carbon removal than marine species, but have a greater range of ability to remove carbon, matching the environmental variability in carbon availability. The diversity of CCMs in seagrasses and marine phyto- plankton, and detailed mechanistic studies on larger aquatic photoautotrophs are understudied. Strengthening the links between ecology and CCMs will increase our understanding of the mechanisms underlying ecological success and will place mechanistic studies in a clearer ecological context.

I hope that we can use this thread to build a library for study and discussion.

 

[Yugang]

Here is one more article that I like, as it has some interesting information on CO2 in natural waters, rivers and lakes, worldwide.

One of my pet projects is understanding why we generally recommend some 30 ppm CO2, and why the range between low tech and high tech, say 10-15 ppm has not got a bit more attention and practitioners in the hobby. So what is the natural environment where our plants come from?

Spatial patterns in CO 2 evasion from the global river network
Ronny Lauerwald, Goulven G Laruelle, Jens Hartmann, Philippe Ciais, Pierre A.G. Regnier

Abstract
CO2 evasion from rivers (FCO2) is an important component of the global carbon budget. Here we present the first global maps of CO2 partial pressures (pCO2) in rivers of stream orders 3 and higher and the resulting FCO2 at 0.5° resolution constructed with a statistical model. A geographic information system based approach is used to derive a pCO2 prediction function trained on data from 1182 sampling locations. While data from Asia and Africa are scarce and the training data set is dominated by sampling locations from the Americas, Europe, and Australia, the sampling locations cover the full spectrum from high to low latitudes. The predictors of pCO2 are net primary production, population density, and slope gradient within the river catchment as well as mean air temperature at the sampling location (r 2 = 0.47). The predicted pCO2 map

was then combined with spatially explicit estimates of stream surface area Ariver and gas exchange velocity k calculated from published empirical equations and data sets to derive the FCO2 map. Using Monte Carlo simulations, we assessed the uncertainties of our estimates. At the global scale, we estimate an average riverpCO2 of 2400 (2019–2826) μatm and a FCO2 of 650 (483–846) Tg C yr1 (5th and 95th percentiles of confidence interval). Our global CO2 evasion is substantially lower than the recent estimate of 1800 Tg C yr1 although the training set of pCO2 is very similar in both studies, mainly due to lower tropical pCO2 estimates in the present study. Our maps reveal strong latitudinal gradients in pCO2, Ariver, and FCO2. The zone between 10°N and 10°S contributes about half of the global CO2 evasion. Collection of pCO2 data in this zone, in particular, for African and Southeast Asian rivers is a high priority to reduce uncertainty on FCO2.

The article has interesting statistics from nearly 1200 samples in global river systems, especially on CO2 release and CO2 concentrations. The first observation is that for our hobby global averages are less meaningful, as (sub)tropical waters usually have much more CO2 than cooler waters.



We usually express our CO2 in ppm, rather than partial pressures, refer therefore to the conversion table on the right.

Here some more detailed data from the model described in the article:



So narrowing in on the regions most relevant for our hobby, most river systems seem to have between 2000 and 5000 MicroAtm partial CO2 pressure, with smaller patches above 5000 Micro Atm. Using the conversions to ppm above, the take away would be the majority between 3.4 and 8.6 ppm, with a minority above 8.6 ppm CO2.

Of course we don't know how our water plants are distributed, and there is a possibility that they are over represented in the CO2 richer waterways. Still, we can argue that the majority of waterways does not even get close to our 30 ppm CO2, not even in the tropics in South America and South East Asia.

Of course, open for discussion.

 

[Marcel G]

I am adding a source here that complements the one above in that it specifies normal CO2 concentrations in the Amazon basin:

The biogeochemistry of the Amazon Basin (2001, McClain) => Amazon.com or libgen.rs
Chapter 15: Organic matter and nutrients in the mainstem Amazon River (pp. 275-306)

 

[Marcel G]

I'm adding another interesting resource on the behaviour of aquatic plants when the carbon source suddenly changes from HCO3 to CO2 (and vice versa):

Rapid inhibition of HCO3− use by high concentration of free CO2 in Elodea canadensis (1993, Adamec)
DOI: 10.1016/0304-3770(93)90031-Q

Abstract

The effect of exposure at a high concentration of free CO2 (denoted henceforth as CO2) in simple bicarbonate media on alkalization (increase of pH) of the media was investigated in the submerged macrophyte, Elodea canadensis Michx., in short-term experiments. Experimental plants were exposed at a high CO2 concentration of 0.45–1.35 mM in bicarbonate media of total alkalinity (TA) 0.3–9.8 mmol/l directly at the beginning of pH-drift experiments. In other cases, the plants were pretreated with 1 mM CO2 for a given period (1–60 min) and exposed afterwards. Plants having been exposed in the media with 1 mM CO2 for 30–60 min alkalized these media to a lesser extent thereafter, i.e. their photosynthetic HCO3− affinity was strongly reduced. The HCO3− compensation point of photosynthesis (carbon-based rates) was about 0.22 mM at pH 10.47 in the untreated controls, but about 0.69 mM at pH 9.60 in CO2-pretreated plants. The pretreated plants showwed a substantial reduction in HCO3− affinity lasting up to 12 h, although a very slow recovery of HCO3− affinity took place during this time. In Ceratophyllum demersum L., however, no marked reduction in HCO3− affinity was found after the CO2 pretreatment. In all measurements, the initial TA of media did not stay constant and dropped by 0.02–0.20 mmol/l. This finding shows that the employment of the pH-drift method is problematic.

I will make some interesting observations from the article:

1) Most HCO3 users (i.e. plants able/habituated to take up carbon from bicarbonate) prefer CO2 to HCO3.

2) HCO3 users take up free CO2 mainly at pH 5-7 in bicarbonate water, whereas at pH values higher than 8.3-8.8, HCO3 use is dominant.

3) High concentration of CO2 inhibits photosynthetic uptake of CO2 and the simultaneous O2 release in many macrophytes, algae and cyanobacteria. The critical CO2 concentration leading to the incipient inhibition of photosynthesis was found to be about 1 mM (= 44 ppm). Specifically, it was in the range of 0.60-0.95 mM (= 26-42 ppm) for 'Egeria densa' and 0.6-0.7 mM (= 26-31 ppm) for 'Elodea canadensis'. Such high CO2 concentrations can also lead to acidification of the cytosol, which can cause some mild reversible damage to the organs ("narcosis").

4) If HCO3 users grow in water with naturally low CO2 concentrations (in the range 0.01-0.07 mM = 0.5-3.1 ppm), then they need to have at least 0.2-0.3 mM HCO3 (= 12-19 ppm) in the water to use these ions for photosynthesis. If they do not have the necessary amount of HCO3 in the water, they become carbon deficient. => This could be an important insight for growing some plant species in acidic water with zero alkalinity (as practiced e.g. by @sudiorca). Just for reference: 1°dKH = 22 ppm HCO3. Thus, one possible reason why some plant species (= HCO3 users) may not grow well under sudiorca's conditions may be the zero (or <20 ppm) HCO3 concentration.

5) If HCO3 users are exposed to even a short-term (±1 h) high CO2 concentration (about 1 mM = 44 ppm), they may lose their ability to use HCO3 due to the very high photosynthetic rate, and it may take days to weeks (!) for them to adapt back to HCO3 use.

PS: Some additional information [you will find here] was obtained directly from the author of this study in private correspondence.

 

[Marcel G]

Affinity for CO2 in relation to the ability of freshwater macrophytes to use HCO3- (1998, Maberly)
DOI: 10.1046/j.1365-2435.1998.00172.x

We may find Table #1 very interesting, where we see the CO2 concentrations at which the studied plants reached "50% saturation of photosynthesis" (which could be rephrased as "50% growth rate" [with a little good will]):


PS: I added "ppm" units in red.

For those of you who don't know scientific language, this means that if you provide the "red" (ppm) CO2 concentration to the plants in question, they will grow at about "half power" (i.e. their growth rate will be about half of their maximum). Almost maximum (~90%) growth rates are reached by most plants at about 2-3 times these values (= 3*K1/2). However, these "red" concentrations should be absolutely sufficient for good growth of these plants (unless you need that super extra fast = maximum growth rates).

I would like to remind in this context the observation from post #4 (point 3) that too high CO2 concentration (~1 mM = 44 ppm) can lead to inhibition of photosynthesis (i.e. to slowing down or stopping of growth, when CO2 starts to have a "narcotic" effect on plants).

For the nitpickers: the "K1/2" does not actually denote "growth rate", but "photosynthetic rate/efficiency". In practice, however, this usually corresponds to growth rate.